This research will be a continuation of a study of changes in the composition and metabolism of basic chromosomal proteins which occur at various stages of spermatogenesis in the rat. Emphasis will be upon the role of acetylation and phosphorylation, in the replacement of the somatic-type histones, H1 and H2b, by the corresponding testis-specific histones, TH1-x and TH2b-x respectively. The effects of gonodotropic hormones and testosterone upon acetylation and phosphorylation of histones will be observed. A study will be made of the possible existence and functions of mediators of the hormonal effects on acetylation of histones. Mononucleosomes will be isolated from the chromatin of seminiferous epithelial cells of the testis to determine whether TH2b-x and H2b occur in the same mononucleosome or whether TH2b-x replaces both molecules of H2b in some of the mononucleosomes.